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Holley/Quick Fuel vs. Demon

91r/t

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Ok, so I understand both the Holley Quick fuel stuff and the BG Demon stuff uses the same jets, but jesus what a difference in jetting out of the box. All the carbs I see people running on a Stroker using a Demon are way fatter jet wise then the Holley/QF stuff. Even out of the box the Demons are fatter than **** compared to the Holley/QF. The 850's that Demon offers other than one are jetted in the mid 80's for primaries and high 80's to low 90's on secondaries while the Holley and QF stuff is usually 76-79 primary wise and mid 80's on the secondaries. Just an overall observation, not getting into a technical war, but just noticed while researching similar engines and jetting, the same can be said about the carbs. Guys running the Holley stuff are usually mid to high 70's on the primaries where all the Demon stuff is low to mid 80's jet wise. Same with secondaries. Do the Demon carbs really not flow fuel as well or something where they need to be jetted fatter? I'd think an 850cfm carb in general that was flow tested by Holley would be set up to flow similar out of the box. **** you find when your bored in the house and the weather sucks for 6 months haha! Just curious why the big swing between the carb brands? Like I said just a bit of observation while looking at a bunch of carbs that are offered through Holley that are supposedly very similar. Anyone ever messed with the two and the flow of fuel between them to see why the big jet difference?
 
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A stroker really shouldn’t need more jet the a normal cube motor, maybe less. Greater cubes move more air, better signal, more fuel. What’s the PVCR size difference between the 2 types? Are there Booster design differences? Those would be the 2 main items in my book.
Doug
 
Yea there's alot of science to it, some of which I don't understand. Just got me thinking when comparing the two. Same booster type and Throttle bore in carb. Most of the carbs were 1.75" bore throttle plates and have downleg booster designs. Some others had the annular boosters but most don't list the venturi sizes which also could be diff I guess. So basically if the carb has the signal to draw more fuel in from the same size jet, as long as the fuel is there it will do so....and more efficiently too?
 
For some reason the demons (referring to the speed demons) run much richer out of the box. Everyone I know that's run one needed to buy the $100 tuning kit to get it right. Step up rod changes are the cure i believe.... as for me I'll stick with my holleys !
 
It depends on which models you compare. Look at venturi and throttle blade size, not so much the cfm.
For example my 850 speed demon (it's an old pre-holley unit) has1.56 venturis with 1.75 throttle blades.

That equates to Holley's 1000HP carb or the 850 UltraXP. Emulsion and the other metering calibration all comes into play.
Holley's site isn't real consistent with it's specs info on each carb though which is kinda lame.


There were complaints about the early demons but mine's been great. It's been drilled/tapped for adjustable bleeds and pvcr's.
My 505 is currently jetted 82/89 and plugs are finally fantastic, pulls 12.2-12.5 at WOT but cruises in the high 13- low 14 range with great throttle response. I've used holleys and have a newer QF but always came back to the 'ol demon, even strictly on butt-dyno results the difference is very noticeable.

.....I just noticed on holley's site the 850 speed demon now comes jetted 70/76 with 1.688 blades. Venturi size not listed.
So Holley's f'd those up too now....
 
It depends on which models you compare. Look at venturi and throttle blade size, not so much the cfm.
For example my 850 speed demon (it's an old pre-holley unit) has1.56 venturis with 1.75 throttle blades.

That equates to Holley's 1000HP carb or the 850 UltraXP. Emulsion and the other metering calibration all comes into play.
Holley's site isn't real consistent with it's specs info on each carb though which is kinda lame.


There were complaints about the early demons but mine's been great. It's been drilled/tapped for adjustable bleeds and pvcr's.
My 505 is currently jetted 82/89 and plugs are finally fantastic, pulls 12.2-12.5 at WOT but cruises in the high 13- low 14 range with great throttle response. I've used holleys and have a newer QF but always came back to the 'ol demon, even strictly on butt-dyno results the difference is very noticeable.

.....I just noticed on holley's site the 850 speed demon now comes jetted 70/76 with 1.688 blades. Venturi size not listed.
So Holley's f'd those up too now....

Is it an annular or dog leg booster?
 
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